ABSTRACT
This chapter deals with a technology that is fully developed on the ground, and naturally fits even better in the low temperature environment of space. Working at the liquid nitrogen temperature prevailing in space, the newly discovered high-temperature superconductors are expected to make rapid inroads into a variety of space applications. For example, it has a high potential for storing large amounts of energy for multi-megawatt burst power systems for space defense. While some barriers are yet to be overcome, these materials have enormous potential for new space and ground-based applications, or merely to expand proven technologies that currently use liquid helium superconductors. Cryogens carried on board for propulsion may be judiciously routed to augment the cooling of new superconductors at selected places on the spacecraft platform. The energy density in the magnetic field is much higher than in an
electrical field. The air can support a uniform E-field of 3.1 kV/mm in a standard atmosphere. Most liquids break down at 10 kV/mm. A liquidfilled capacitor operating at 3.5 kV/mm has a stored energy density of U ¼ 1=2"E2 ¼ 1=2(2 8.88 10 –12) (3.5 106) ¼ 108 J/m3 between the electrode plates. The energy storage density in magnetic field is given by U ¼ 1=2BH ¼ 1=2B2/mo. An air-cooled copper coil with a current density of 1.5A/mm2
producing a 2 tesla B-field would store U ¼ 1=2 22/(4 10 –7) ¼ 1.6 MJ/ m3 in the hollow of the coil. This is four orders of magnitude higher than the energy density in the E-field. A superconducting coil carrying much higher current density would result in an even higher energy density in the square proportion of the magnetic field density. Commercial superconducting magnets are available at present to produce a 5 to 15-T field over 1/100 to 1 liter volume for a variety of applications. They yield an energy density of 40MJ/m3 at 10 T and 90MJ/m3 at 15 T.
